Finally got tired of screwing around with my trailer lights and replaced everything from the connector back. Rewired everything. Not only grounded the trailer, but ran a seperate 12 guage ground wire to each light. Replaced the tail lights and the "cross member" light bar with the new LED units along with the side marker lights. WHAT A DIFFERENCE!!!!!!! These LED's are brighter in the daylight than my old "normal" lights were at night. Completely waterproof, rated for 100,000 hours with a ten year guarantee. I got nine whole months out of my last "submersible" incandescent units. What a joke. If you're having light problems, go with the LEDs. They are more than worth it.

Formula
I'm in the process of doing that very thing myself. I just added a drive guard to my MYCO trailer so I had to rewire anyway. One thing that I did, that people behind me will hate at night is, instead of the little 2 or 2.5 inch center marker lights, I used three 4 inch round tail/brake/turn lights and wired them to the CHMSL (center high mounted stop light) circuit of the trailer wiring harness. For the outside tail/brake/turn lights I used the ovals on a 45 degree angle, two on each side. That means when I hit the brakes, people behind my will be looking at SEVEN LED brake lights. Should get people's attention Hopefully this ain't illegal.